Thanks GE, good info there. I love the discussion on AOA going on over there. It's always a confusing topic!
AoA is not really confusing. And the article did an excellent job of explaining it, including the fact that AoA meters are not calibrated for degrees, but rather a more generic measure typically labeled as just "units." Normally, you can find some sort of conversion chart in your operating manual that can easily convert the units to actual degrees, but when it comes down to it, it doesn't really matter. If the tactics are taught using the units, then you are really just comparing apples to apples.
The AoA is primarily designed to ensure the optimal angle upon touchdown on the carrier deck. It's prime advantage over simply using aircraft deck angle is that AoA also provides very useful feedback on whether the aircraft is in danger of stall. So, you get two really nice advantages in just one display.
Where people get confused is forgetting that AoA is the angle of the wing to the airstream. Aircraft deck angle is the angle of the fuselage centerline to the horizon. Most of the time, these two values line up with each other. But, sometimes they get out of alignment. Perhaps the most easily explained, and visually easy to see, example of this potential difference is a jet trying to pull out of a high speed dive. Before the jet starts to level out and then climb, it first tilts the fuselage and wing upward. So, the deck angle of the airplane is positive long before the AoA turns from negative (the descent) to positive (the climb). At some airshows, this is confirmed by seeing pilots pull out too late and end up pancaking onto the ground even though the nose is pointing upward.
The second critical factor is glide slope (also known as glide path), which is always relative to the landing surface, in this case the ship. There are many different visual glide slope measuring devices and the Navy uses the "meatball" for carrier landings. For those who may be confused by this, think of glide path as a stiff wire projected on a three degree angle from the intended touchdown point strung out along the final approach course. If a model plane was connected to two metal loops which were strung up on that glide path "wire" and you released the model, it would slide down the wire until it touch downed on the landing surface. To mimic the Navy carrier landing, simply rotate the model to a three degree AoA/deck angle, lower its "landing gear" and watch is touchdown and land every time.
To simplify it, if you are on AoA and on glide path, then you are assured of a perfect touchdown since the Navy spends considerable money and effort to ensure their landing gear systems on their carrier aircraft can routinely handle whatever touchdown force happens when touchdown takes place on AoA and glide path. Navy pilots are taught to line up both the AoA and the glide path to the perfect alignments. The AoA sensor tells the pilot the AoA value and the meatball tells the pilot the glide path. The Navy can carry out the pinpoint touchdowns because the pilot never flares to lower descent rate.
So, why do pilots on other aircraft flare? Simple, their landing gear are not stressed to handle the sort of touchdown forces encountered if you touchdown at the same vertical velocity encountered when on a standard 3 degree glide path. So, you flare to reduce that touchdown force taking advantage of ground effect which lowers the stall speed and you use the cushion of air under the wings to soften the touchdown. Since you land on longer runways on the ground, you can safely trade longer landing runs for softer touchdowns.
Ken
